Continuous, steady-state, chromatographic separation of gadolinium isotopes

Abstract

A method and apparatus for the partial or complete continuous separation of isotopes of gadolinium, especially high thermal neutron capture cross-section gadolinium isotopes, using continuous, steady-state, chromatography in which an ion exchange resin is the stationary phase, an aqueous solution of ions based on a mixture of gadolinium isotopes is the feed phase, and an aqueous acid eluant solution is the mobile phase. The method involves the mobile phase eluting or desorbing the gadolinium isotopic solute or ligand adsorbed on the stationary phase under conditions such that each of the various naturally occurring isotopes of gadolinium is primarily eluted in an elution volume distinct from the elution volumes of the other isotopes. In a preferred embodiment, the conditions are such that at least one of the elution volumes contains essentially only one isotope of gadolinium. The method is preferably conducted in a continuous, steady-state manner, and it is preferably conducted in a single operation in a continuous annular chromatograph (CAC).

We claim: 
     
       1. A continuous, steady-state, chromatographic method for the separation of each of the isotopes of gadolinium to produce substantially pure fractions of each of the gadolinium isotopes, comprising the steps of: (a) subjecting a feed phase solution of gadolinium ions to continuous, steady-state, annular chromatography using a cation exchange resin as the stationary phase and an eluant solution as the mobile phase; and,   (b) collecting simultaneously a separate isotope for each of the isotopes present in the feed phase.   
     
     
       2. The method of claim 1, wherein said mobile phase is an eluant acid selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, butyric acids, phosphoric acids, oxalic acid, citric acid and acid halides. 
     
     
       3. The method of claim 2, wherein said mobile phase is nitric acid. 
     
     
       4. The method of claim 1, wherein said stationary phase comprises ion exchange resin beads having an average particle size between about 0.1-10 microns and a monodisperse particle size distribution. 
     
     
       5. The method of claim 4, wherein said resin beads have an exchange capacity of between 0.01 and 0.5 milliequivalent for gadolinium ions. 
     
     
       6. The method of claim 1, wherein the separation factor of a chromatographic column in said continuous annular chromatograph for a theoretical stage having a height of 25 cm for the separation of Gd 155  and Gd 157  is at least about 1.05. 
     
     
       7. A continuous, steady-state chromatographic method for the simultaneous separation of each of the isotopes of gadolinium to produce substantially pure fractions of increased thermal neutron capture cross-sections, comprising the steps of: (a) subjecting a feed phase solution of gadolinium ions to continuous, steady-state, chromatography using an ion exchange resin as the stationary phase and an eluant solution as the mobile phase;   (b) collecting simultaneously at least two gadolinium product fractions, one enriched in Gd 155  isotope and the other enriched in Gd 157  isotope; and,   (c) combining the at least two gadolinium product fractions to yield gadolinium product having increased thermal neutron capture cross-sections.   
     
     
       8. The method of claim 7, wherein the continuous, steady-state chromatography is effected in a continuous annular chromatograph. 
     
     
       9. The method of claim 8, wherein the stationary phase is a cation exchange resin. 
     
     
       10. The method of claim 9, wherein the mobile phase is selected from the group of acids consisting of nitric acid, sulfuric acid, hydrochloric acid, butyric acids, phosphoric acids, oxalic acid, citric acid and add halides. 
     
     
       11. The method of claim 10, wherein the mobile phase is nitric acid. 
     
     
       12. A continuous, steady-state, gadolinium isotope separation method, comprising the steps of: (a) loading a stationary phase into a circumferential annular space of a continuous annular chromatograph having an effective column height sufficient to resolve each of said gadolinium isotopes into a distinct product fraction having a sufficient purity, the stationary phase comprising an ion exchange resin having a monodisperse particle distribution of substantially spherical resin beads;   (b) preparing an aqueous feed solution of gadolinium ions from a mixture of gadolinium isotopes;   (c) preparing an eluant solution capable of displacing gadolinium ions from said ion exchange resin;   (d) rotating said annular space of said continuous annular chromatograph;   (e) feeding said feed solution containing gadolinium ions into the top of said annular space so that the feed solution penetrates no more than about 5% of the effective column height of the stationary phase before elution is initiated;   (f) feeding said eluant solution into the top of said annular space to cause each of the gadolinium isotopes in said feed solution to pass down the annular space at different speeds;   (g) collecting a separate product fraction at separate product ports at the bottom of said continuous annular chromatograph, said product fractions corresponding to each of the high thermal cross-section gadolinium isotopes present in the feed solution after elution of all of the gadolinium isotopes present in the feed solution   (e) continuously repeating steps (e) to (g) to produce commercially useful quantities of the high thermal neutron cross-section gadolinium isotopes.   
     
     
       13. The method of claim 12, wherein the collecting step (g) includes at least two separate product ports for collecting at least Gd 155  and Gd 157  isotopes having high thermal neutron capture cross-sections. 
     
     
       14. The method of claim 13, further comprising the step of: (f) combining the Gd 155  and Gd 157  isotope product fractions to yield a thermal neutron capture cross-section enriched gadolinium product.   
     
     
       15. The method of claim 12, wherein the eluant of step (c) is nitric acid. 
     
     
       16. The method of claim 12, wherein the stationary phase of step (a) is a cation exchange resin.